This invention relates generally to magnetic resonance imaging systems and methods and more particularly to radially simultaneous acquisition of spatial harmonics (radial SMASH) systems and methods.
Magnetic resonance imaging (MRI) is a technique that is capable of providing three-dimensional imaging of an object. An MRI system includes a main magnet that provides a magnetic field, gradient coils and radio frequency (RF) coils, which are used for spatial encoding, exciting and detecting nuclei of the object for imaging. The object to be imaged is positioned in a homogeneous field region located in an air space between poles of the magnet. The gradient coils and the RF coils are typically located external to the object to be imaged and inside the geometry of the main magnet.
One technique for decreasing imaging time has concentrated on increasing speed of sequential scanning of a k-space in which the object is located and thus acquisition of MR data by reducing intervals between scanned lines in a slice of the object. Two recent techniques, SMASH technique in a time domain or the k-space and Sensitivity Encoded (SENSE) technique in a frequency domain, changes such sequential data acquisition into a partially parallel process by using an array of detectors, thereby reducing scan time as compared to the sequential data acquisition technique. In the SMASH and SENSE techniques, it is recognized that the data sampled below the Nyquist sampling rate can be recovered if sensitivity profiles of the detectors of the array can provide enough spatial information to either interpolate the data in the time domain or unwrap the data in the frequency domain. The SMASH technique uses a numerical fitting routine to interpolate a decimated number of phase encoding steps and thus, achieve reductions in scan time. There is described in U.S. Pat. No. 5,910,728. However, in the SMASH and SENSE techniques, a maximum aliasing fold that can be unwrapped is limited to the number of detectors in the array.
In one aspect, a magnetic resonance imaging (MRI) method is described. The method includes simultaneously acquiring partial radial backprojection signals from a cylindrical array of m detectors surrounding an object, generating, in a k-space, additional backprojection signals with decimated b-fold backprojection steps. The generating includes producing 2-dimensional (2D) spatial harmonics to replace the decimated b-fold backprojection steps. The producing includes assuming that a sum of weighted sensitivity profiles of at least one of the detectors is a function of an angle between a vector k and an axis kx of the k-space and a function of a radius of a cylindrical surface formed by the array of detectors. The angle is an angle along which reconstruction of an image of the object is performed.
In another aspect, a system is described. The system includes a signal detection device having a cylindrical array of m detectors surrounding an object and configured to simultaneously acquire partial radial backprojection signals from the cylindrical array, and a controller electrically connected to the signal detection device. The controller is configured to generate, in a k-space, additional backprojection signals with decimated b-fold backprojection steps. To generate the additional backprojection signals the controller is configured to produce 2-dimensional (2D) spatial harmonics to replace the decimated b-fold backprojection steps. To produce the 2D spatial harmonics, the controller is configured to retrieve from a memory a sum of weighted sensitivity profiles of at least one of the detectors that is a function of an angle between a vector k and an axis kx of the k-space and a function of a radius of a cylindrical surface formed by the array of detectors. The angle is an angle along which reconstruction of an image of the object is performed.
In yet another aspect, a magnetic resonance imaging (MRI) system is described. The MRI system includes a magnetic resonance (MR) signal detection device having an array of m detectors surrounding an object and configured to simultaneously acquire partial radial backprojection signals from the cylindrical array, and a controller electrically connected to the MR signal detection device. The controller is configured to generate, in a k-space, additional backprojection signals with decimated b-fold backprojection steps. To generate the additional backprojection signals, the controller is configured to produce 2-dimensional (2D) spatial harmonics to replace the decimated b-fold backprojection steps. To produce the 2D spatial harmonics, the controller is configured to retrieve from a memory a sum of weighted sensitivity profiles of at least one of the detectors that is a function of an angle between a vector k and an axis kx of the k-space and a function of a radius of a cylindrical surface formed by the array of detectors. The angle is an angle along which reconstruction of an image of the object is performed.